Self-locking fastener assembly and method of making same

ABSTRACT

A fastener assembly includes a threaded fastener having a head and an at least partially threaded shaft extending from the head, an annular washer encircling the shaft adjacent to the head and a gel patch adhered to the shaft next to the washer, the gel patch extending from the shaft far enough to overlap the washer. A method of making the assembly is also described.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to fasteners. It relates especially to a self-locking fastener assembly especially adapted to secure together components of play structures, furniture and the like, as well as to a method of making the assembly.

2. Background Information

Structures such as wood and metal play gyms, climbing towers, forts, table and chair sets, etc. are often composed of several wood or metal members secured together by bolts and/or other threaded fasteners. Often these structures are sold in a knock-down condition for assembly by the ultimate purchaser. However, the threaded fasteners used in these structures have a serious drawback in that they can become loosened unintentionally after the structure has been assembled and in use if the fasteners were not installed correctly in the first place. For example, a bolt may back off from its nut due to movement of the structure over time if a washer is not present on the bolt. The consequences of this are usually inconvenient, costly and may present serious legal implications for product warrantees.

Indeed, research has shown that many customers do not bother to install the flat washers and spring lock washers that are provided with each structure when erecting that structure. Each structure is designed to have those components present and without them, or when those components are installed incorrectly, the structure can loosen and become a safety hazard. The short-term effect of this is possible injury to the user and the long-term effect is that the designed life of the structure may be jeopardized.

We are aware of fastener assemblies comprising a bolt having a pre-installed washer thereon, the washer being retained on the bolt by striking the bolt shaft to form raised metal upsets behind the washer. However, these are disadvantaged because they require a heavy stamping machine to create the raised upsets and oversized holes in the workpiece to accommodate those raised upsets.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a self-locking fastener assembly for wood, plastic and metal structures.

Another object of the invention is to provide a fastener assembly comprising a threaded fastener with a pre-installed washer thereon.

Another object of the invention is to provide such an assembly whose washer does not separate from the associated fastener during handling.

A further object of the invention is to provide a self-locking fastener assembly which may be color-coded for ease of sorting.

Still another object of the invention is to provide an assembly of this type whose washer can be preinstalled on and secured to its fastener on a high volume production basis.

A further object of the invention is to provide a method of securing a washer to a threaded fastener to form a self-locking fastener assembly.

Other objects will, in part, be obvious and will, in part, appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the article possessing the features, properties and the relation of elements which are exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.

Briefly, the subject fastener assembly comprises threaded fastener having a head and a threaded shaft or shank, and a washer installed on the shaft under the head. The washer is retained on the shaft by a gel patch applied to the shaft under the washer and then cured to form a relatively stiff yet resilient body which projects out from the shaft so as to overlap the washer. To secure two beams or other members together, the fastener shaft, if tapered to a point, may be inserted through a hole in one member and screwed into the other member. On the other hand, if the fastener is a bolt, the bolt shaft may be inserted through aligned holes in both members and a nut turned down onto the threaded end of the bolt shaft. In both cases, the washer will distribute forces exerted by the fastener head over a relatively large area of the adjacent member and if the washer is a lock-type washer, such as a spring washer, the washer will exert a lengthwise force on the fastener head that tends to prevent the fastener from rotating. Resultantly, the two structural members will remain fastened together even when subjected to vibration or other forces in use.

As we shall see, the silicon gel patch is applied as a liquid to the fastener using specially designed equipment capable of high-speed operation and then cured, preferably using ultraviolet light, to hold the washer permanently in place on the fastener.

The present fastener assembly thus assures that every play or furniture structure is safe from customer error by insuring that the very important washers are installed in every unit. The assembly also reduces the chances of washers being lost from the hardware bags that accompany the product thus reducing the number of customer service calls concerning missing hardware and attendant UPS charges to ship replacement parts.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary perspective view showing a play structure whose members are held together by fastener assemblies incorporating the invention;

FIG. 2 is a perspective view of a much larger scale showing the fastener assembly in greater detail, and

FIG. 3 is a diagrammatic view showing the method of making FIG. 2 assembly.

DESCRIPTION OF THE PREFFERED EMBODIMENT

Refer to FIG. 1 of the drawings which shows a segment of a top rail R, comprised of parallel wood beams R₁ and R₂, of a children's play gym that supports a swing shown generally at S. Swing S is suspended from rail R by way of a pair of brackets B clamped to opposite sides of rail R by fastener assemblies shown generally at 10. These fastener assemblies not only secure brackets B to rail R, but they also clamp together the two rail sections R₁ and R₂ comprising that rail.

As shown in FIG. 2, each fastener assembly 10 comprises a threaded fastener 12 having a head 12 a, and a shaft 12 b at least part of which is threaded as shown at 12 c. The illustrated fastener 12 is a bolt. Therefore, shaft 12 b is of uniform diameter and only the free end segment thereof is threaded. However, the fastener could also be a screw-type fastener in which case the shaft 12 b would be tapered to a point and may be threaded along substantially its entire length.

Assembly 10 also includes a washer 14 installed on shaft 12 b adjacent to head 12 a. The illustrated washer 14 is a split spring washer. However, it could just as well be a lock washer, Bellville washer, flat washer, etc. In any event, the washer is held in place on shaft 12 b by a silicon gel patch 16 applied to the side of the shaft on the other side of the washer from head 12 a. In the case where the fastener 12 is a bolt as illustrated in FIG. 2, the fastener assembly may also include a nut 18 adapted to be threaded onto the threaded part 12 c of the bolt.

The gel patch 16 is applied to shaft 12 b as a liquid and then cured, preferably by exposure to ultraviolet light. A suitable silicon material of this type is available from Locktite Corporation. When fully cured, the gel patch constitutes a relatively stiff, rubbery solid body. The gel patch 16 is stiff and large enough to overlap the washer thereby permanently retaining washer 14 on fastener 12. However, when the fastener is installed as shown in FIG. 1 and the nut 18 is turned down on the end of the fastener, the gel patch 16 tends to compress against and frictionally engage the adjacent surface of bracket B helping to prevent bolt 12 from rotating as nut 18 is tightened on the bolt.

To help secure nut 18 on fastener 12, the threaded part 12 c of the fastener may be coated with an adhesive 22 which utilizes the turning or twisting action of the nut to break or sheer micro-capsules containing resin. The resin initially acts as a lubricant assisting in the installation of the nut. Within about twenty-four hours, however, the resin will cure to its designed maximum holding strength. An adhesive of this type is available from 3M Corporation under the designation Scotch Grip Pre-applied Adhesive.

Preferably also, the resin capsules are color-coded to facilitate sorting the fastener 12 by size, e.g. a yellow color indicates a one-quarter (¼) inch bolt, a blue color indicates a five-sixteenths ( 5/16) inch bolt, etc.

Refer now to FIG. 3 which illustrates how the washer 14 and gel patch 16 are assembled to fastener 12. At the beginning of the assembly line, fasteners 12 in a bin 22 are deposited in turn on a conveyor 23. Simultaneously, washers 14 from a bin 24 are deposited on a conveyor 25. The conveyors convey those components toward a bolt/washer assembly station 26. On the way, the fasteners are centered in turn directly over successive washers 14 at station 26 and are dropped through those washers. Each fastener/washer subassembly is then conveyed by conveyor 24 to a gel application station 28 at which a gel applicator 30 applies a small tab of liquid silicone 16′ to the side of the fastener shaft 12 b just under the washer 14. The liquid silicone is viscous enough so that it remains in place on the shaft until that subassembly is carried by conveyor 25 to a gel set station 32. Station 32 contains a UV light source 34 with an overlying hood 24 a and which illuminates each fastener/washer subassembly conveyed to station 32 with light rays L having a wavelength which causes the liquid silicone 16′ on that assembly to set. Thus, by the time that assembly leaves station 32, a stiff but resilient gel patch 16 is adhered to the fastener thereby forming the complete assembly 10. The complete assemblies are then collected in a bin 36 for further processing.

As will be seen from the foregoing, assembly 10 can be made very efficiently on a high volume production basis so that the overall cost of the assembly is kept to a minimum.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the construction set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein. 

1. A fastener assembly comprising a threaded fastener having a head and an at least partially threaded shaft extending from the head; an annular washer encircling the shaft adjacent to said head, said washer having a side facing away from the head, and a gel patch adhered to the shaft adjacent to said side of the washer, said gel patch extending from the shaft far enough to overlap the washer.
 2. The assembly defined in claim 1 wherein the fastener is a bolt, and said shaft has a threaded end segment.
 3. The assembly defined in claim 2 and further including a nut turned down on said threaded end segment of the shaft.
 4. The assembly defined in claim 1 or 2 wherein the washer is a lock-type washer.
 5. The assembly defined in claim 1 or 2 wherein the washer is a spring-type washer.
 6. The assembly defined in claim 1 and further including adhesive microcapsules coating the shaft threads.
 7. The assembly defined in claim 6 wherein the microcapsules are color-coded to indicate the size of said fastener.
 8. A method of making a self-locking fastener assembly comprising the steps of advancing fasteners each having a head and a threaded shaft extending therefrom in succession to a first assembly station; advancing washers each having a hole therein, in succession, to said first station under said fasteners; at said first station, aligning successive fasteners and washers so that each fastener can be deposited in the hole of an underlying washer; advancing successive fastener/washer subassemblies from said first station to a second station and at said second station applying dabs of liquid plastic to the sides of the shafts of successive subassemblies under the washers thereof; advancing the dabbed subassemblies, in turn, to a third station where each successive subassembly is subjected to electromagnetic energy which solidifies the liquid plastic dab thereon to form a raised resilient patch which overlaps and retains the washer on the fastener of each successive subassembly to form a self-locking fastening assembly, and transporting the successive self-locking fastener assemblies from the third station to a collection location.
 9. The assembly defined in claim 8 including the additional step of selecting the succession of washers from the group consisting of plain washer, lock-type washer and spring-type washer.
 10. The method defined in claim 8 including the additional step of coating the shaft threads with adhesive microcapsules.
 11. The assembly defined in claim 10 including the additional step of color-coding said microcapsules on each shaft to indicate the size of the associated fastener. 